First demand drives up prices of existing land, then government further drives up the prices of existing land by upzoning, which literally makes the plots able to be "larger" (ie able to support a greater Floor to Area Ratio, FAR) and more valuable.

Note, in this case, the process took about 15 years. In my understanding, that is about how long ago those who owned property in Crown Heights began to petition the city for a rezone. This rezone was finally passed last year:

In Harlem, real estate brokers who are impatient with how slowly the local businesses are changing are literally opening their own coffee shops to improve the value of the properties they are trying to sell.